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How wireless vehicle detection can get you out of a jam

It was great to catch up with so many traffic signal engineers at last month’s JCT Traffic Signal Symposium. The discussions throughout the symposium got us thinking once again about how much money could be saved and congestion reduced with an alternative approach to traffic light management.

For signalised junctions to control the flow of traffic most effectively, they need to know where the traffic is and how far the queue extends at traffic lights. This information enables the use of adaptive traffic light control such as MOVA and SCOOT. Inductive loops have traditionally been used to detect vehicles at such junctions, but the introduction of wireless vehicle detection sensors in 2009 has provided an alternative that allows local authorities to benefit from huge cost savings.

But how do wireless vehicle detection systems work?

Wireless vehicle detection systems use magnetometer sensors to measure the earth’s natural magnetic field and detect deviations from this reference when a vehicle passes over it. The sensor communicates wirelessly using a unique radio protocol to an Access Point installed on the signal head. This lets the junction know where the traffic is waiting, just as traditional inductive loops do.

No method of vehicle detection is 100% accurate, but, in a trial by TfL assessing base line accuracy, the magnetometer sensor was more precise in detecting vehicles than traditional inductive loops.

So wireless vehicle detection is as or more accurate than inductive loops, but the wireless communication and the small size of the sensor make it easier to install. Herein lie the many benefits of this approach—these sensors are less expensive and quicker to install, and require less maintenance than inductive loops.

So how can local authorities benefit from these savings?

Solutions such as the M100 Wireless Vehicle Detection System do not require any ducting and trenching. This means that installation costs are massively reduced, especially for junctions using SCOOT or MOVA traffic signal control, which require detection either on the exit of a junction or well in advance of a stop line; and so need a significant amount of ducting to reach the loops furthest from the junction. This issue for loops is compounded in urban areas where ducting needs to be dug by hand to avoid utilities and other infrastructure. Conservative estimates suggest this can cost at least £100 per metre. Add this to capital costs and ducting solutions quickly become prohibitively expensive.

But the costs don’t end there. Where loops are used in high traffic areas they are prone to failure when the surface of the road degrades or other contractors cut through the loops. These failures lead to significant maintenance costs.

In contrast, wireless vehicle detection sensors are installed in a small 100mm x 50mm hole in the centre of the carriageway that requires no specialist slot cutting, ducting or trenching. This simpler installation means that the sensor can be installed in a matter of minutes, one lane at a time, so traffic can keep flowing and disruption is minimised. The central placement of the sensor also means it is much less prone to damage.

When upgrading three busy junctions to MOVA, Blackburn with Darwen Borough Council made savings of over £60,000 just in installation costs by using the M100 wireless vehicle detection system instead of loops.

Benefits were also felt by Aberdeen City Council when they transitioned to wireless vehicle detection. Within the city, the life of the inductive loop could be as short as three to five years, leading to extensive maintenance costs. Neale Burrows, Technical Officer of the Intelligent Transport Systems Unit commented: “The installation of the M100 sensor is much quicker than cutting new loops, which is important to us given the high profile and busy urban locations of the junctions involved. Traffic disruption is minimal and traffic management costs and duration are significantly reduced.”

A large number of other authorities have benefited from the reduced initial capital and overall lifetime costs of the M100 system, including: Transport for London, Shropshire County Council, Lincolnshire County Council, Reading Borough Council, City and County of Swansea and many motorway junctions for Highways England.

Don’t miss out, when you are specifying your next signalised junction upgrade consider both inductive loops and wireless vehicle detection to understand how much you could save.